Railway traffic controlling apparatus



July 17, 934. 7 H. A. 'II'HOMPSON RAILWAY TRAFFIC CONTROLLING APPARATUS Original Filed Oct. 16, 1950 4 Sheets-Sheet l A ATTORNEY July 17, 1934; H. A. THOMPSON 1,966,939

RAILWAY TRAFFIC CONTROLLING APPARATUS Original Filed Oct. 16, 1930 4 Sheets-Sheet 2 INVENTOR 1 b Fl i H Q, .WW

A ATTORNEY JURY 11?, 3934. H, THOMPSON 1,966,939

RAILWAY TRAFFIC CONTROLLING APPARATUS Original Filed Oct. 16, 1930 4 Sheets-Sheet 5 E C INVENT? ATTORNEY July 17,1934. THOMPSON 1,966,939

RAILWAY TRAFFIC CONTROLLING APPARATUS Original Filed Oct. 16, 1930 4 Sheets-Sheet 4 INVENTOR A ATTORNEY Patented July 17, I934 T FlC RAILWAY TRAFFIG CONTROLLING APPARATUS Howard A. Thompson, Edgewood, Pa., assignor to The Union Switch &

Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application October 16,

1930, Serial No. 489,065

Renewed March 18, 1933 33 Claims.

My invention relates to railway traffic con.- trolling apparatus utilizing coded current in track circuits for the control of either or both wayside and cab signals in an absolute permissive block signaling system.

I will describe one form of apparatus embodying my invention and will then point out the novel features thereof in claims.

The accompanying Figs. l 1 1 and 1 when placed end to end with Fig. l on the left, form a diagrammatic view showing one form of apemoodying my invention when applied to a stretch of single track railway extending between two passing sidings designated by the reference characters P1 and P2.

In describing my invention, reference is made to the accompanying rawings wherein like characters of reference designate corresponding parts with an exponent added to the reference charcter to designate the location. I shall assume he left-hand end of each figure to be west and the right-hand end of each figure to be east, and I shall speak of a train traveling from the right to the left as a westbound train and one traveling from the left to the right as an eastbound train.

The traflic rails l and 2 are arranged in track sections A--B. B-C, (3-D, by the usual insulatsd rail joints. The track sections AB and C-D are arranged with a cut section at the points Al and D1 respectively. It will be understood however that arrangements of track sections other than that here disclosed may be employed without departing from the scope of my invention.

The energy for the operation of the apparatus is furnished by transformers L, one of which is located at each junction of adjacent track sections. The primary 4 of each of these transformers is connected to a transmission line E which is constantly supplied with alternating current of a convenient commercial frequency such as cycles per second from a source not shown in the figures. An auxiliary transformer M located at eachjuncticn of adjacent track relay designated by the reference character TR.

The secondary 16 of each track transformer connected across the rails of the associated track section through the usual current limiting reactance 17.

The primary 29 of each track transformer T is supplied with alternating current from an associated line transformer which current is periodically interrupted coded at the rate of 8G or 180 cycles per minute or any other code frequency desired under c tain traffic conditions; while under other tr on in the specifications.

affic conditions, the alternating current is noncoded, all of which will be fully described later Each track relay TR is a two element relay having a track element 8 connected, in series with a secondary 9 of impedance transformer 1T, across the rails the track section at the end opposite from the track transformer. The second element 11 each track relay is constantly supplied with of altel-hating current from the secondary 6 of the associated line transformer L. Connected connected in such .a manner that it does not respond tothe coded energy when supplied the associated code feeding transformer CF.

The particular function of the track relay,

associated impedance transformer and the code feeding transformer will be brought out in detail as the description progresses.

It follows that when any given track section is unoccupied, the track relay of that section is normally operated by the 18 0 code alternating current supplied to the rails at the opposite end of the section.

At each junction of adjacent track sections,

there is provided a code transmitter CT which includes a motor element 25 constantly supplied with alternating current by the secondary 6 the line transformer L at that location. This code transmitter is to be of any of the standard 1 types commonly used and as here shown it will he understood that the four upper contacts (see Fig. 1 36, 37 and 38, periodically cl their respective front and back contacts at a rate of times per minute and that the four lower contacts 39, 40, 41 and i2 periodically close their respective front and back contacts at a rate-of 30 times per minute.

Each track relay controls decoding appara including a transformer DT, a rectifier" DR. and a decoding relay TP. The primary 43 (see location A of Fig. 1a) of each of the transformers DT is supplied with direct current by the associated rectifier B through an armature .4 of the track relay TR. When the track relay TR is energized, current from the positive terminal of rectifier R flows along wire 45, armature 44 in engagement with its front contact, the righthand half of primary 13 of transformer lDT to a center tap and wire 46 to the negative terminal of rectifier R When relay TR is deenergized and armature 44 in engagement with its back contact, then current from rectifier R flows through the left-hand half of the primary 43 of transformer lDT- It follows then that with the ck relay 'I'R operated by a coded current and its armature 44 alternately in engagement with its front and back contacts, an alternatng voltage is induced in the secondary 47 of the transformer lDT the frequency being the same as the frequency of operation of a track relay, but when the track relay TE is continuously energized or is continuously deenergized, no voltage is induced in the secondary 4'7. The secondary 4'7 is connected to the input terminals of the rectifier IDR while the terminals of the decoding relay lTP are connected to the output terminals of the rectifier lDP, as will be readily understood from the figure. The decoding circuit being non-tuned, it fol lows that with the track relay TR being alternately energized and deenergized in step with the 180 code, the relay lTP is energized, while with the track relay l'lR remain ng either continuously energized or deenergized, the decoding relay lTP is deenergized.

At each junction of adjacent track sections, there is provided for each direction of trafiic, a slow-acting relay designated by the reference character 1P where the relay is associated with eastbound traffic and 2P where the relay s associated with the westbound trafiicv Referring to the slow-acting relay lPA, current to energized this relay is supplied by the secondary 6 of the line transformer L over a circuit consisting of wires 12 and 5'7, armature 58 of the relay lTP wire 59, armature 60 of a line control relay 1H to be referred to later, wire 51, relay 1PA and wires 62 and 14 to the common terminal of the secondary 6. All slow-acting relays of my invention are controlled by a circuit similar to that just traced for the slowacting relay lPA, except for a slight modification at all intermediate signals as will shortly be pointed out.

At all intermediate locations, the slow-acting relays IF and 2? are associated with a thermal unit TU, which retards the pick-up of the relay and which is connected into the circuit whenever the relay is deenergized. Referring to the relay lPC of Fig. 1 it is to be noted that this relay is normally held energized by a circuit including a back contact 145 of the opposing directional relay 2V and the front contact of its own armature 63. To close this stick circuit for relay 1P0 it is requ red that the associated thermal unit lTU must first be heated to close the contact 65. As soon as the heating element 66 heats up so as to close contact 65, a pick-up circuit is established through the contact 65 to the relay 1P0. With relay 11 C once up, it closes its stick circuit at the front contact of armature 63 and opens the circuit to the heateas es ing element 66 at the back contact of armature 63.

At the junction of adjacent intermediate track sections, there are provided two directional stick relays designated by the reference character 1V and 2V with an exponent corresponding to the location. These stick relays perform similar functions to those performed by the directional stick relays used in standard absolute permissive block systems-that is, to establish dir ctional control and to permit following train movements. As the circuit for selecting the directional relay is the same at each location of my invention, only one location will be described. Referring to location C of Fig. 1, directional relay 1V has a pick-up circuit consisting of secondary 6 of the line transformer L wire 67, armature 68 of the relay 2P0 down in engagement with its back contact, wire 69, armature 70 of relay 2T5 down in engagement with its back contact, wire '71, armature 72 down in engagement with its back contact, wire '73, armature '74 in engagement with its front contact, wire '75, relay 1V and wire '76 to the common terminal of secondary 6. The stick circuit for this directional relay 1V extends from the wire 6'7 along wire '77, armature '78 of relay lTP in engagement with its back contact, wire '79, armature of relay 1V up in engagement with its front contact and wire 81 to the wire '75 and then to the coil of the relay 1V There exis also a second path for this stick circuit for relay 1V that branches from wire 67, through back contact 144 of relay lPC and to the wire '79.

At the junction of adjacent track s ctions there is also provided for each direction of traific a line control relay. The line control relays associated with trafiic from the left to the right in the figures are designated by the reference character 1H with an exponent corresponding to the location; while the relays associated with trams from the right to the left are designated by the reference character 2H with an exponent correspondin to the location. Each of these line control relays is a three position polarized relay governing the operation of an associated wayside signal in accordance with standard A. P. B. signaling. Referring to the line control relay 11%, the element 48 is constantly supplied with alternating current from the secondary 6 of the transformer L by means of wires 12 and 13 on one side and by wire 14 to the other terminal. The second element 49 of the relay 1H is normally supplied with alternating current from the secondary 6 of the transformer L by the circuit that extends from one terminal of the secondary 6 of L along wire 50, armature 51 of relay iPB, wire 52, armature 53, line wire 54, element 49, wire 14, common line wire 18 and wire 56 to the other terminal of secondary 6 of L Under normal or clear traffic conditions, the instantaneous polarity of the current energizing the two elements 48 and 49 of relay 1H is such as to cause the contact armatures of the relay 1H to swing to the left-that is, to the position shown in the Fig. 1 With the relay 1P3 deenergized so that its armature 51 is in engagement with its back contact and with the directional relay 1V energized so that its armature 82 is up in engagement with its front contact, the element 49 of relay lHA is supplied with current by a circuit extending from the center terminal of winding 5 of the transformer M along wire 56, common line wire 18, wire 14, element ac, line wire 54, armature 53, wire 52, armature 51, wire 83, armature 82 and wire 84 to a negative terminal of the winding 5 of transformer M Under this condition and with the winding 5 of M functioning as an auto transformer, the instantaneous polarity of the current energmng element 49 of relay 1H is opposite to that of the current energizing the ele- 48 and it follows that the contact armatures of the relay ll-l will be reversed to the right-hand position-that is, a position 0pposite to that shown in the Fig. 1 It will be understood that with either element 48 or 49 deenergized,--the armatures of the relay ll-I will assume a vertical or mid-position. Each line relay of my invention is controlled in a manner similar to that just described for the relay lll Each track section is provided with a wayside signal located at each end of the section and signals govern trafiic in opposite directions through the section. Signals governing traffic from the left to the right in the figures are desi nated by the reference character 18 with an exponent corresponding to the location, wlnle the signals governing traffic from the right to the left are designated by the reference character 2S with an exponent corresponding to the location. These wayside signals may be of any standard type and are here shown as the threeposition light signal type. The lighting circuits of each signal are controlled by the associated line control relay and as the lighting circuits of all signals are alike, a description of any one wil sufficient for the understanding of all. Refer-Log to the signal 15 the proceed light circuit extends rom one terminal of secondary 6 of transformer L along wires 12, 26 and 86, armature 8'7 of relay 11 A raised into engagement with its front contact, wire 88, armature 39 of ne control relay 15 in the left-hand position, wire 90, proceed light 91 of signal 1S and wires 92 and 14 to the common terminal of the secondary 6. The caution light circuit is the same as that just traced for the proceed circuit up to the armature 89, and with arma ture 89 in the right-hand position it extends along wire 93, caution light 94 and wires 92 and 14 to the common terminal of 6. The stop light circuit is the same as that traced for the proceed light up to armature 8'7 and then with armature 87 down in engagement with its back contact, it extends along wire 95, stop light 95 and wires 92 and 14 to the common terminal of 6,

At intermediate track sections equipped with but one track circuit such as the track section BC, a slow-release floating tracl: relay N is provided in order to provide proper operation of the directional stick relays at that location. A tr nsformer 9? has its primary 98 connected across the track leads of the track transformer TB, while the secondary 99 of the transformer 97 is connected to the input terminals of the rectifier l o, the output terminals of which are connected to the relay N Belay N being slow-releasing, it follows that its armature will remain lifted so long as the primary of a track transformer TB is fed with coder energy or with non-coded alternating current, but with the transformer TB not suppli d with then the relay NB becomes deenergized.

Having pointed out the various devices with which my invention is provided, I Will now describe its operation and I shall first assume that all track sections between the two sidings are unoccupied. Normally coded alternating current is supplied to each track circuit by the track transformer. Refer 'ing to the track circuit for the section A-Al, the primary 20 of the track transformer TAl has one terminal connected to the common terminal of secondary 5 of the line transformer L by the common line wire 18 and wire 14, while the other terminal of the primary 20 is connected to the other side of the secondary 6 by the line wire 22, armature 23 of the relay 1T wire 24, 180 code contact 38 of the code transmitter GT and wires 26 and 12. It follows then that the track relay TR. normally follows each 180 code cycle, alternately closing the front and back contacts of its armature 44. As pointed out earlier in the descrip" tion, the positive terminal of the rectifier R is connected to the heel of the armature 44 by a wire 45 and the extreme ends of the primary 43 of the decoding transformer lDT are con nected to the front and back contacts of the armature 44; while the center tap of the primary 43 is connected to the negative terminal of the rectifier R by a wire 46. Therefore with armature 44 alternately closing its front and back contacts, the half of the primary winding of the decoding transformer fed by the front contact will be energized for the duration of the on code period building up a flux in one direction and when the off period of the code cycle occurs and the back contact closes, the other half of the primary 43 will be energized in a reverse direction from that of the first. This action will cause the flux to build up in the first instance and to die down and build up in the reverse direction with each 180 code cycle. With the building up of the flux in one direction and the dying down and building up in the 0pposite direction, a voltage is induced in the secondary 4? of the transformer 133T said voltage having a corresponding frequency. As the secondary 47 is connected to the input terminals of a rectifier IDE to whose output terminals the relay l'lP is connected, and, inasmuch as the circuit is non-tuned, the relay 1T]? is normally energized. With relay lTP normally en ergized so that its armature 58 is in engagement with its front contact, the circuit to the relay IPA is held closed and thus the relay lPA is also normally energized. Inasmuch as all track circuits function alike, we see, therefore, that the track circuit of each track section is normally supplied with 180 code energy and that this energy is decoded to energize the TP relay and in turn permits the energizing of the 1? or the 2P relay at that location. It will be noted that the circuit for the primary 20 of the track transformer TAl is controlled by the front contact of the armature 23 of the decoding relay lTP which in turn is controlled by the track circuit fed by this track transformer. It follows then that once the track circuit to the primary of the track transformer is opened f Or in the event that traffic conditions are such that the line relay 1H is reversed and armature 28 is in engagement with its reverse contact then this circuit extends along the wire 32, to the code contact 42 of the code transmitter CT Again, in the event the line relay 1H is deener gized and its armatures occupy a mid-position, then the circuit extends from the wire 101 along wire 31, armature 30, wires 33, 26 and 12 directly to the secondary 6 of the transformer L It will thus be seen that the track circuit for the section A-A1 when unoccupied is continuously supplied with 180 code energy and that once the track section becomes occupied then the current supplied to the track circuit may be either continuous alternating current, or 80 code current, or 180 code current as governed by the line control relay in accordance with the different traffic conditions to be later described.

Referring to the impedance transformer 1T and the code feeding transformer CP associated with the track relay TE the Wire 103 is permanently connected to one side of the primary 104 of the code feeding transformer CF and also to one side of the primary 105 of the impedance transformer 1'1 and this wire 103 connects these transformers to the heel of the armature 106 of the decoding relay 11?. The opposite side of the primary 104 is permanently connected to the common terminal of the secondary 6 of the line transformer L by the wire 14. As as the section A-A1 is unoccupied so that the relay lTP is energized, these transformers 1T and CF are connected through the front contact of the armature 106 and a wire 107 to the 180 code contact 36 of CT and thence by wires 26 and 12 to the other terminal of the secondary 6. It is to be noted that the other terminal of the p-imary 105 of 1T is connected to the back contact of 180 code contact 36 by the wire 108. The 180 code contact 36 operates in unison with the 180 code contac 38 which feeds coded energy to the primary 20 of the track transformer TAl. When the code contacts 36 and 38 are in their upper position, wire 107 is connected to the secondary 6 and when contacts 36 and S8 in their lower position this wire 107 is connected to wire 108 and the primary 105 is thereby short-circuited. Thus when the code transmitter is in its upper position, energy is fed to the primary winding 104 of the code feeding transformer CF the primary 105 of the impedance transformer 1'1 is open circuited, and the primary 20 of the transformer TAl is also open circuited. When the code transmitter is in its down position, the primary 20 of the track transformer 'IAl is receivin. energy, the primary 164 of the code feeding transformer CP is disconnected and the primary 135 of the impedance transformer 1'1" is short-circuited so that the energy from the secondary 20 of the tracl; transformer TAl may flow freely to the winding 8 of the track relay TR to energize that relay. When the code transmitter CT is in its up position and the secondary 3 of the code feeding transform CP is supplying energy to the rails, the p mary 105 of transformer lT is open circuited and thus the secondary 9 offers relaively high impedance to the now of energy from the secondar through the element 8 of the track relay Furthermore the current supplied by the secondary 3 to the track leads is in the reverse direction from that supplied by the normal track transformer TAl and it follows that whatever small energy" reaches the element 8 from the secondary 3 is in a direction to open the relay TB With the relay l'I'P deenergized so that the armature 106 is in engagement with its back contact, the primary 104 of CF is supplied with 180 code energy over a circuit from the secondary 6 of line transformer L wires 12 and 26, 180 code contact 36, wire 109, normal contact of the armature 110 of line control relay 211 wire 111, armature 112 of relay 2PA, wire 113, back contact of the armature 106, wire 103, primary 104 and wire 14 to the common terminal of the secondary 6. In the event that traffic conditions are such that the line control relay ZH is reversed. and its armature 110 in engagement with its reverse contact or that the armature 112 of the relay 2PA is in engagement with its back contact, then the code feeding transformer CF is supplied with 80 code energy through the 80 code contact 40 of the code transmitter CT along the Wire 114, armature 112 and wire 113, and then as before traced, or else by the 80 code contact 40 along wire 11 1, armature 110 reversed, wire 111, armature 112 up, wire 113 and as before traced.

With each circuit supplied with coded energy at each end of the section in a manner similar to that just described for the track circuit of section AAl, it lecomes apparent that the coded track current affords a means for controlling Wayside signals governing traffic in either direction. It also affords means for supplying cab signal controlling current to the to control ti current inductively from the track rails such as the apparatus described and claimed in the Letters Patent of the United States, No. 1,773,472 filed by P. N. Bossart on the 7th day of February, 1927.

I will not describe the operation of the apparatus for a train moving from the left to the right-that is, an eastbound train and I shall assume that the train occupies the track section to the left of a location A and that the intermediate sections to the passing siding P2 are all unoccupied. With the train occupying the track circuit to the left of A, the slow acting relay 2PA is deenergised With the result that the signal 2S indicates stop and the signal ZS indicates caution. As the train advances to the right and enters the track circuit A-Al, the track relay TB and in turn relays lTP and IPA all be come deenergized and the wayside signal IS caused to display a stop signal. The deenergization of the lTP relay opens the line circuit for the line control relay 2H at the front contact of armature 115 and thus the signal 28 is set at stop. In like manner each successive westbound signal up to the passing siding P2 is set at stop. The track transformer TAl will continue to supply to the rails of AAl, 180 code energy by a circuit extending from the secondary 6 of L along wires 12 and 26, 180 code contact 38, wire 24, wire 29, armature 28, wire 101, armature 23, wire 22, primary 20, common line wire 18 and wire 14 to the common terminal of secondary 6. his 180 code energy in the rails of the section A-A1 will establish a proceed cab signal on the train. As the train advances and passes the cut section A1 and en tore the track circuit of A1B, it shunts the track relay TR and in turn the relay TP is deenergized with the result that the line control relay 1H now becomes deenergized due to its in carried apparatus receivline circuit being opened at the armature 53 and thus the wayside signal 13 still displays a stop signal. The deenergization of relay 1H cuts off 180 code energy fed to transformer 17111 at the contact 28. The code feeding transformer CF now supplies the rails of A1B with 180 code energy to establish a proceed cab signal. The circuit by which the code feeding transformer CF supplies 180 code energy to the rails of Al-B is from the secondary 6 of the transformer L wire 50, 180 code contact of CT wire 117, armature 118, wire 119, armature 120 in engagement with its back contact, wire 121, primary 122 of code feeding transformer CF and wires 123 and 56 to the other terminal of the secondary 6.

It is to be noted that when the relay lTP is deenergized, the primary 105 of the impedance transformer 1T is short-circuited through a back contact of the code transmitter CT by a shunt path extending from primary 105 along wire 193, back contact of the armature 106 of relay 1TP wire 113, armature 112 in its raised position, wire 111, armature 110 of the line relay 2H wire 109, back contact of the 180 code contact 36 and Wire 108 to the other terminal of the primary 105. In the event that the relay ZPA is down, then the shunt extends from the armature 112 along wire 114, back contact of i the 30 code contact and to wire 108. In the case where armature 112 is up and the armature 110 of relay 21% is reversed, then this shunt path also is by way of the back contact of the 88 code contact 40.

As the train vacates the section A-A1, noncoded alternating current is supplied to the transformer TAl by a circuit as follows: secondary 6 of transformer L wires 12, 26 and 33, deenergized contact of armature 30 of relay 111 wires 31 and 101, back contact 23, wire 22, primary 20 of transformer Th1 and wires 18 and 14 to the other terminal of the secondary 6. This non-coded alternating current flows in the track element 8 of the relay TE and due to the periodic shunting of the primary 105 of the impedance transformer 1'I by one of the paths just traced and which paths include a code contact of the code transmitter C'I it follows that the current value in the element 8 will be periodically varied. When the shunt is closed, the secondary 9 of 1T offers relatively low impedance and the current in 8 is of sulficient value to lift the armature 44 of the relay TR When the shunt is opened at the code contact of transmitter CT, the secondary 9 offers a relatively high impedance and the current in the element 8 is reduced to a value where the armature 44 drops. Thus by this varying of the effective impedance of the secondary 9, track relay TR is caused to operate on code although the track transformer T111 supplies non-coded current to the track circuit. After a few operations of the armature 44, the decoding relay' lTP- is reenergized and'as soon as its armat re 23 is lifted, 180 code current is supplied to the track transformer "IAl, as under normal conditions. Any following east" bound train that might enter the section A- A1 while the first eastbound train occupies the section AL-Bwill receive only non-coded alternating current. The energization of the relay lTP closes the front contact at the armature 154 with the result that current is then fed to the line circuit for the eastbound signal to the rear of signal 153 and this signal to the rear of IS will thus display an approach signal as soon as the track section A-A1 is -vacated.

As the train enters the section B-C, the track relay 1TB is shunted and the track repeater relay 2TP is deenergized to open the line circuit to the primary of the track transformer TB at the front contact of the armature 124. The floater relay N being also shunted, becomes eenergized and closes the back contact of the armature 125. The line control relay 1H and the repeater relay lPB both become deenergized when the track circuit of BC is shunted. It is arranged that the relay N will drop and closes the back contact 125 before the armatures of the relay 11 B disengage their front contacts and thus the pick-up circuit for the directional relay 1V becomes closed. The pickup circuit for the directional relay IV is similar to that traced earlier in the description for the directional relay 1V With the directional relay 1V once up, then its stick circuit is closed and the relay remains energized after the relay lPB drops. This deenergization of the line relay 11-1 and the picking up of the directional relay 117 results in the signal 1S displaying a stop indication and the signal 1S displaying an approach indication.

As the train enters the section B-C, the primary 146 of the impedance transformer 1T is short-circuited by a shunt path extending from one side of the primary 146 along wire 121, back contact of the armature 120 of the relay TP wire 119, back contact of the armature 118 of the relay llT-B, wire 143, front contact of armature 142, wire 141, back contact of code contact 39 of the code transmitter GT and wire 14? to the opposite terminal of the primary 146. As the train va'cates section A1B, the line relay 2H having been reenergized, coded energy is supplied to the track transformer 'IBl through the back contact 130 of the decoding relay TP and the polar armature 155 of the line relay 211 The track relay TR is now operated on code in as much as a code impulse will occur during the interval that the primary 146 is short-circuited and thus the relay TP is reenergized with the result that the normal circuit for supplying 180 code energy to the track transformer TBl is restored. In the event that a second eastbound train is following, the second train holding the line relay 21-1 deenergized, then non-coded energy is supplied to the transformer TBl after the first train vacates the section Al-B, the circuit being from the secondary 6 of the transformer L along wire 50, deenerglzed contact of the armature 125, wire 127, back contact of the armature 128, Wire 129, back contact of the armature 130, line wire 131, primary 20 of transformer 1331, the common line wire 18 and wire 56 to the other terminal of the secondary 6. Due to the above described shunt path on the primary 146 of the impedance transformer 1T the secondary 9 of the transformer 1T offers low impedance to the non-coded current supplied to the track element of the track relay TR during the period that the shunt path is closed at the 80 code contact 39, and a relatively hgh impedance during the period that the shunt is opened. It follows that the track relay TR will be operated on code as the result of the variation of the eifective impedance of the secondary 9 and thus the track relay will operate to reenergize the decoding relay TP in the same manner as that described for the relay TR The reenergization of the decoding relay TP restores the normal circuit by which 180 code is fed to the transformer T131. It is to be noted that the circuit for supplying noncoded energy to the transformer TBl includes a back contact of the 128 armature of the relay TR The energization of the relay TR during the interval that the shunt on the transformer 1T is closed will act to open this circuit for supplying non-coded energy to the track transformer at the armature 128 and this action will also produce an alternate raising and dropping of the armature of the track relay TR to thereby assist in the prompt energization of the decoding relay TP This last feature however is used further under westbound traffic conditions as will be pointed out later. As the relay TP is reenergized and the armature 129 raised, the shunt on the primary 146 that was previously traced is disconnected and the primary 146 is alternately opened and closed at a back contact of the 180 code contact 35 of the code transmitter C'I as is done under the normal condition of the track circuit.

As the eastbound train vacates the section BC, the line relay 211 having become energized, coded current is supplied to the track transformer TB for the section B-C. This circuit includes a back contact of the armature 124 of the relay 2TP and the armature 156 of the relay 21-1 and thus the track circuit for the section BC is restored to 180 code energy. In the event that there is a following eastbound train and the relay 2H is held deenergized, th n non-coded current is supplied to the track transformer TB after the first train vacates the section B-C. However, the train by shunting the track circuit of the section C-Dl provides a shunt path on the primary of the impedance transformer 1T which shunt path is similar to that traced for the transformer 1T and which includes a contact of the code transmitter CT". The result is that in this case the relay l'IT-t is operated by means of varying the effective impedance of the transformer 1T in the same manner as has been previously described for the track relays 'IR and. TR with the result that the track circuit for the section 13-0 is restored to 180 code energy.

As the train travels in the section B-C, 180 code energy is supplied to the rails by the code feeding transformer CF over a circuit extending from the secondary 6 of the line transformer L along wire 67, 180 code contact 35 of code transmitter CT wire 133, armature 134, wire 135, back contact of armature 135, wire 137, primary of the code feeding transformer C15 and wire 138 back to the secondary 6 and this 180 code energy will establish a proceed cab signal. I have above pointed out how a caution signal is displayed by the wayside signal 1S during the time that the train occupies the track section BC. In the event that a following train enters the section A-A1 and shunts TR to drop relay lTP code energy is supplied to the rails by the track transformer TAl by a circuit previously traced and which includes the 80 code contact 42 of the code transmitter CT and the reverse contact of the armature 28 of the line control. relay 1H Thus as this following train enters and travels in the section AA1, 80 code energy is supplied to establish a caution cab signal. Should the following train advance and enter the section Al-B while the first train still couples the section BC then 80 code energy is supplied to the rails of the section Al-B by the code feeding transformer CF over a circuit extending from the secondary 6 of transformer L along wire 50, 80 code contact 39 of code transmitter CT wire 141, armature 142 in engagement with the front contact, wire 143, armature 118, wire 119, armature 120, wire 121, primary 122 and wires 123 and 56 back to the secondary 6. This 80 code energy supplied to the rails of the section A1-B will establish a caution cab signal on this following train.

As the train which I have assumed to be traveling from the left to the right travels in the successive track sections, the operation will be similar to that described in connection with the track sections AB and B-C.

To sum up the operation of an eastbound train, it is found that as the train enters each section, coded alternating current is applied to the rails at the exit end of the section to effect operation of the cab signals, this coded current being of a code determined by 'trafiic conditions in advance. The track circuits are restored either by applying coded current as soon as the train vacates the section or, in the event iat there is a second train following, by applying non-coded current to the rails and then varying the impedance of the circuit at the relay end which eifects the resetting of the track circuit. All opposing wayside signals in advance of the train are held at stop, and the eastbound signals to the rear of the train are governed according to the usual practice.

The operation of the apparatus as a westbound train travels from the passing siding P2 towards the passing siding P1 is similar to that described for the operation of the eastbound train. except for certain differences in the method of resetting the track circuits which will now be pointed out.

Assuming that a westbound train travels in the section B-C, the normal active transformer TB will supply coded current to the rails to effect operation of the cab carried devices. As the westbound train vacates the section B-C and efiects the deenergization of the line relay 2H non-coded alternating current will be sup plied to the transformer TB. In the event that there is no following westbound train, the relay lPC will have been picked up as the train vacated the section C-Dl and with the relay 11C up to close the front contact of the armature 134 there exists a shunt path around the primary of the impedance transformer 1T that includes wire 152, the 180 code contact 35 of the code transmitter C'I wire 133, armature 134, wire 135, armature 136 down and wire 137. The periodic opening and closing of this shunt path at the 180 code contact 35 brings about the operation of the track relay lTR by the non-coded current being supplied by the track transformer TB. 'As a result, the decoding relay ZTP is reenergized and the track circuit for section BC restored to 185 code energy. I In the event that a second westbound train is fol-- lowing and the relay 1P0 is deenergized thereby. a shunt is placed around the primary of 1T that includes wire 152, armature 153 of 1V down, armature 134 down, wire 135, armature 136 down and wire 137. Inasmuch as this shunt path is not periodically opened and closed, the non-coded current supplied to the transformer TB would pick up the relay 1TH and hold it up were it not for the fact that the circuit for gized supplying the non-coded current to the transformer TB includes the back contact of the 128 armature or" the relay lTR The result is that the pickup circuit for relay 1TH is opened once this relay is energized. It follows that the armature of the relay lTl-t will be alternately lifted and dropped. After a few such operations, the decoding relay will be energized and once it is energized, the track circuit is restored to 18: code energy. The restoring of the track circuit for the section A1B to 180 code energy as the westbound train travels and vacates that section will be similar to that just described for the section BC.

As the westbound train vacates the section A-A1, the relay lI-i will be reenergized it there is no following train and with 11? energized, coded energy is at once supplied to the transformer TAl with the result that the decoding relay lTE' is reenergized and the circuit restored to its normal condition. If there is a following westbound train and the relay 1H is deeperthereby, then non-coded energy is supplied to the transformer TAl. There exists however, a shunt path on the primary of 1T that includes the code contact 40 of the code transmitter CT and a back contact of the armature 112 of the relay EPA. The periodic variation of the impedance of the secondary 9 by the opening and closing of this shunt path with ro uce an operation of the track relay TR that reenergizes the decoding relay lTP and restores the track circuit of section A-A1 to 18% code.

To sum up the operation for westbound traific, it is found that coded energy is supplied at the exit end of each track section to effect operation of the train carried cab signals. By means of the line relay H, the opposing eastbound signals in advance of the train are held at stop. The track circuits are restored to the normal condition of 180 code energy either by supplying coded energy as soon as the track section is vacated or in the event that there is a following train by first applying non-coded current and periodically interrupting the circuit or else by varying the effective impedance of the track circuit at the relay end.

Such a system herein disclosed and described is practically immune from propulsion alternating c rrent or direct current, or any other form of electrical energy that may be used in the running rails. Furthermore, such a system will operate equally as Well for wayside signals alone or traincarried cab signals alone or for both wayside and cab signals.

It will be understood that the train gov 'ning rail current which I use for the purpose or train detection, that is, for the purpose of indicating the presence or absence of a train within a track section by means of wayside equipment, as well as the rail current which I use for the control of cab signals, are not confined to alternating current, nor to current or" the periodically interrupted type. Obviously, the coded. current used for detection and cab signal control may be either alternating or direct, the only requirement being that the periodic variations in this current be of such character as to permit the code iollowing track relay to follow, and at the same time to produce suitable response of the cab signaling devices on the train.

Although the 188 code which I use for detection purposes is the same as the .86 code used for clear cab signals, it will be understood that any other code suitable for operating the code following track relays may be used. That is, a separate and distinct code may be used for detection purposes, use of the 180 code for this pr rpose being made primarily to avoid the necessity for additional apparatus such as code transmitter and relay contacts. Since the track relays are sufilciently quick acting to follow the fastest of the cab signal codes, a reset or trans fer from the cab signal code to the detection code may be obtained on any of the cab signal control codes, determined by tranic conditions. The cab signal control code can, of course, be used to operate any train-carried governing devices other than cab signals, or in addition thereto. For example, this code may be used to control speed governing apparatus, if desired.

Although I have herein shown and described only one form of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my in vention.

Having thus described my invention, what I claim is:

1. In combination, a track section, a wayside signal located at each end of the section to govern trailic in opposite directions through the section, a line relay for each signal to govern the operation of the signal, means to normally supply to the rails of the section train governing alternating current periodically interrupted, a track relay connected to the rails and responsive to such periodically interrupted alternating current, a decoding relay, means associated with the track relay to energize said decoding relay when the track relay is operated by the interrupted alternating current, and means responsive to the energizing of the decoding relay to render each line relay effective to clear its associated wayside signal.

2. In combination, a track section, a wayside signal located at each end of. the section to govern traffic in opposite directions through the section, a line circuit for each signal, a circuit controlling device controlled by each line circuit to govern the operation of the associated signal, means to normally supply to the rails of the section train governing alternating current periodically interrupted, a track relay connected to the rails and responsive to such riodically interrupted alternating current, a decoding relay, means associated with the track relay to energize the decoding relay when the track relay is operated by the interrupted alterne 'ig current, and means responsive to the ener icing oi the decoding relay to render each circuit controlling device effective to clear associated signal.

3. In combination, a track section, a track circuit for said section including the trafiic rails, means located at the exit end of the section to normally supply alternating current periodi' cally interrupted at different rates to the track circuit, a track relay connected to the rails normally responsive to said periodically interrupted alternating current, a polarized line relay, means controlled by the track relay of another track. section to effect normal and reverse positions of said line relay, and a polarized armature controlled by the polarized line relay to select the different rates of the periodically interrupted current.

e. In combination, a track section,

a track circuit for said section including the traffic rails, means to normally supply alternating current periodically interrupted to the track circuit, a track relay conn cted to the rails and normally responsive to said periodically interrupted alternating current, a decoding relay, means asso ciated with the track relay to energize the decoding r ay when the track relay is operated by the interrupted al nating current, a polarline relay, means controlled by the decoding relay oianot er track section to effect normal and reverse positions of said line relay, a wayside signal having a proceed and a caution operating circuit, and a polarized armature controlled by the polarized line relay to selectively control the operating circuits.

5. In combination, a track section, a track circuit for said section including the trafiic rails, -c .s to normally supply alternating current periodically interrupted at different rates to the track circuit, a track relay connected to the rails and normally responsive to said periodically interrupted alternating current, a decoding relay, means associated. with the track relay to energize the decoding relay when the track relay is operated by interrupted alternating current of any one of said difierent rates, a polarized line relay, means controlled by the decoding relay or another track section to eifect normal and reverse posi ens c. said line relay, a wayside signal having a proced and a caution operating circuit, a first polarized armature controlled by the polarized line relay to selectively control the operating circuits, and a second polarized. armature controlled by the line relay to select the different rates of the periodically interrupted current.

6. A combined wayside and cab signal system for railways including, a track section, two wayside signals located so as to govern traffic in opposite dl'ections through the section, a line circuit for each wayside signal to control the operation of the signal, means at each end of the section to normally supply to the rails traingoverning alternating current periodically interrupted at different rates, a track relay responsive to such interrupted alternating current and. connected to the rails at one end of the section, means to permit the operation of said track relay by the interrupted alternating current supplied to the rails at the end opposite the relay and to prevent its operation by the interrupted current supplied to the rails at the same end as the relay, decoding means controlled by the track relay when operated by the interrupted current to control the said line circuits, and means rendered effective by a train traveling through the section in either direction to select the rate of interruptions of the alternating current supplied to the rails at the end in advance of the train in accordance with trafiic conditions ahead.

7. A combined wayside and cab signal system "ways including a track section, two waynals located so as to govern traffic in opposite directions through the section, a line circuit for each Wayside signal to control the operation of the signal, means at each end of the section to normally supply to the rails coded alternating current of codes to produce difierent cab indications, a track relay responsive to coded alternating current and connected to the rails at one end of the section, means to permit the operation of said track relay by the coded alternating current supplied to the rails at the end opposite the relay and to prevent its operation of the relay by the coded current supplied to the rails at the same end as the relay, decoding means controlled by the track relay when operated by coded alternating current to control the said line circuits and thereby control the wayside signals, and means rendered effective by train traveling through the section in either direction to select the code supplied to the rails at the end in advance of the train in accordance with traffic conditions ahead and thereby control train carried cab signals.

8. A combined wayside and cab signal system for railways including, a track section. two wayside signals located so as to govern traffic in opposite directions through the tr ck section, means at each end of the section to supply to the rails alternating current periodically interrupted at difiercnt rates to produce diiierent cab indications, a track relay connected to the rails at one end of the section and responsive to such periodically interrupted alternating current, means to normally permit the operation of the track relay by the interrupted current supplied to the rails at the end opposite the relay and to prevent the operation of the track relay by the interrupted current supplied to the rails at the same end as the relay, a decoding relay, means associated with the track relay to energize the decoding relay when the track relay is operated by interrupted alternating current of any one of said diiTerent rates, means rendered eil'ective with the decoding relay energized to govern the operation of each of said wayside signals; and two means, one for each direction of traillc each of which is responsive to trarhc conditions in advance of the track section for its respective given direction of trailic, and rendered efiectlve With the decoding relay deenergized to select the rate of the periodically interrupted alternating surrent supplied to the rails at the exit end of the track section for its respective direction of traflic and thereby selectivel control train-carried cab signals.

9. A railway signal system, including a stretch of single tracl: railway arranged in track sections, a first signal located at one end or" the stretch to govern traffic in one direction through the stretch, a second signal located at the other end of the stretch to govern traffic in the other direction through the stretch, a line circuit for each signal to control the operation or the signal, a source of train governing coded alternating current for each section located at one end and arranged to normally supply coded alternating current to the rails, a track relay for each section connected to the rails at the end opposite the source and responsive to coded alternating current, a decoding relay for each section, means associated with each track relay to energize the decoding relay cf the section in respons to the track relay operated by the coded alternating current, and means controlled by each decoding relay to control the line circuit of each of said signals.

10. A railway signal system including a stretch of single track railway arranged in track sections, 2. first signal located at one end of the stretch to govern traflic in one direction through the stretch, a second signal located at the other end of the stretch to govern traffic in the other direction through the stretch, a line circuit for each signal to control the operation of the signal normally closed to establish proceed signal, a source of train governing coded alternating current located at each end of each section each arranged to normally supply coded alternating current to the rails, a track relay for each section responsive to coded alternating current and connected to the rails at one end of the section, means to normally permit operation of the track relay of each section by the coded alternating current supplied to the rails at the end opposite the relay and to prevent the operation of the relay by the coded alternating current supplied to the rails at the same end as the relay, and means controlled by each track relay to control the line circuit of said signals and to control the supply of train governing coded alternating current at each end of the associated track section.

11. A railway signal system including a stretch of single track railway arranged in track sections, a signal located at-each end of the stretch to govern traffic in opposite directions through the stretch, a line circuit for each signal to control the operation of the signal normally closed to establish a proceed signal, a source of train governing coded alternating current located at each end of each section each arranged to normally supply coded alternating current to the rails, a track relay for each section responsive to coded alternating current and connected to the rails at one end of the section, means to normally permit the operation of the track relay of each section by the coded current supplied to the rails at the end opposite the relay and to prevent the operation of the relay by the coded current supplied to the rails at the same end as the relay, and means controlled by the track relay of a section effective when a train occupies the section traveling in either direction to open the line circuit of the opposing signal and to discontinue the normal supply of the train governing coded alternating current to the rails at the exit end of each track section for a train traveling in the opposite direction.

12. In combination, a track section, two wayside signals located so as to govern trafiic in opposite directions through the section, a line relay for each signal, a slow acting relay associated with each line relay, means jointly controlled by a line relay and its'associated slow acting relay to govern the operation of the associated signal, a source of current located at each end of the track section, coding means associated with each current source each adapted to normally supply train governing coded current to the rails of the section, a track relay responsive to such coded current and connected to the rails at one "end of the section, means to normally operate the track relay by the coded current supplied to the rails at the end opposite the relay and to prevent the operation of the relay by the coded current supplied to the rails at the same end as the relay, a decoding relay, means to energize the decoding relay in response to the track relay operated coded current, a first circuit means controlled by the decoding relay to control the slow acting relay located at the same end as the track relay and the line relay located at the opposite end to thereby control the signals, and a second circuit means controlled by the decoding relay to control the supply of train governing coded current at each end'oi the track section.

13. In combination, a track section over which traffic may move in either direction, a signal located at each end of the section to govern traffic in opposite directionsthrough the section,

a line relay for each signal, a slow acting relay and a directional relay associated with each line relay, means jointly controlled by a line relay and its associated slow acting relay and normally supply train governing coded current i to the rails of the section, a track relay responsive to coded current connected to the rails and arranged to be operated by the coded current supplied by one of said coding means only, a decoding relay, means associated with the track relay to energize said decoding relay in response to coded current supplied to the track relay a first circuit means controlled by the decoding relay to control the slow acting relay located. at the same end of the section as the track relay and the line relay located at the opposite end of the section to thereby govern the operation of the signals, a second circuit means controlled by the decoding relay to govern the supply of coded train governing current at each end of the track section, and a third circuit means controlled by the decoding relay to control the two directional relays of the section.

14. In combination, a track section, an alternating current transmission line, a signal located at the entrance end of the track section, a line circuit associated with said signal, a polarized alternating current relay having one winding connected to said line circuit and a second winding constantly supplied with current from the transmission line, an auto-transformer located at the exit end of the section having a winding one half of which is the primary receiving current from the transmission line, means controlled by trafiic conditions in advance to connect under certain trailic conditions one-half of the winding of said auto-transformer to the line circuit and under other traffic conditions to connect the other half of said winding to the line circuit to thereby effect a normal and a reverse position of the line relay, and operating circuits for the signal controlled by said line relay.

15. In combination, a track section, an alternating current transmission line, means located at the exit end of the section to supply to the rails train governing alternating current periodically interrupted at different rates, a line circuit, a polarized alternating current relay havrent from the transmission line, an auto-transformer having a winding one-half of which is the primary receiving current from the trans ing one winding connected to said line circuit and a second winding constantly supplied with curmission line, means controlled by traffic conditions in advance of the section to connect under certain traffic conditions one-half of the winding of said auto-transformer to the line circuit and under other traffic conditions to connect the other half of said winding to the line circuit to thereby effect a normal and a reverse posi- T supply each track circuit with said coded alternating current, a decoding relay for each track relay, means to energize said decoding relay in response to its track relay operated by coded alternating current, a signal located at each end of the track section to govern traiiic in opposite directions through the section, and means controlled by the decoding relays to control the operation of said signals and to control the supply of the coded alternating current to said track circuits.

1'7. In combination, a track section, a track transformer located at the exit end of the section, a supply circuit to Supply train governing coded alternating current to the track transformer, a track relay responsive to said coded alternating current located at the entrance end of the section, a decoding relay, means associated with the track relay to energize said decoding relay when the track section is unoccupied and the track relay thereby operated by the coded alternating current and to deenergize the decoding relay when the track section is occupied and the track relay thereby shunted, means controlled by said decoding relay to close said supply circuit when it is energized and to open said supply circuit when it is deenergized, and a line control relay responsive to traffic conditions in advance of the section to render said decoding relay ineffective to open said supply circuit under clear traflic conditions.

18. In combination, a track section over which traflic may move in either direction, means to supply current periodically interrupted to the trafiic rails of the section, a track relay connected to the traffic rails and responsive to such periodically interrupted current, a decoding relay, means to steadily energize the decoding relay when the track relay is operated by the periodically interrupted current, a normally energized slow releasing relay responsive to traflic conditions of the track section and of an adjacent track section, a normally deenergized directional stick relay, a pick-up circuit for said stick relay including a front contact of the slow releasing relay and a back contact of the decoding relay, and a circuit controlled by said stick relay for controlling the supply of interrupted current of another track section.

19. In combination, a track section over which traflic may move in either direction, a source of track circuit current connected to the traflic rails at one end of the section, a track relay connected to the traff c rails of the section at the end opposite the source, a normally energized slow releasing relay controlled by the track relay, a floater relay connected across the track leads of the source of track circuit current and normally energized, a normally deenergized directional stick relay, a pick-up circuit for the stick relay including a front contact of the slow releasing relay and a back contact of the floater relay, and a signaling circuit closed only when said stick relay is energized.

20. In combination, a track section over which traffic may movein either direction, a source for supplying current periodically interrupted and connected to the traffic rails at one end of the section, a track relay connected to the rails of the section at the end opposite the source and responsive to such periodically interrupted current, a decoding relay, means for steadily energizing the decoding relay when the track relay is operated by the interrupted current, a normally energized slow releasing relay controlled by the decoding relay, a floater relay connected across the track leads of the source of interrupted current and normally retained steadily energized, a normally deenergized directional stick relay, a pick-up circuit for said stick relay including a front contact of the slow releasing relay and a back contact of the floater relay, and a circuit controlled by said stick relay for controlling the supply of interrupted current of another track section.

21. In combination, a signaling circuit for railways, a source for supplying said circuit with non-coded current, a code-following relay con nected to the said circuit at a point remote from said source, a traffic controlled means located adjacent said relay to code the current supplied by said circuit to the code following relay, a decoding relay, means associated with the code following relay to energize the decoding relay in response to code operation of the code following relay, and traffic governing means controlled by said decoding relay.

22. In combination, a track section, a track circuit for the section including the track rails of the section, a source of current connected to the rails at one end of the section to at times supply said track circuit with non-coded current, a code following track relay connected to the track rails at the end of the section opposite the said source, traffic controlled means located adjacent the track relay and connected in the track circuit between the track rails and the track relay and adapted to code the non-coded current supplied to the rails, a decoding relay, means associated with the track relay to energize the decoding relay in response to code operation of the track relay, and traffic governing means controlled by the decoding relay.

23. In combination, a track section, a first source to normally supply alternating current periodically interrupted to the track rails at one end of the section, a track relay connected to the track rails at the opposite end of the section and alternately energized and deenergized by the periodically interrupted alternating current, traific controlled means to disconnect the first source and to connect a second source to supply to the rails a non-interrupted alternating current, means located adjacent the track relay to periodically vary the impedance of the connection between the rails and the said track relay to effect an alternate energizing and deenergizing of the track relay when supplied with current from the said second source, and means controlled by the track relay when alternately energized and deenergized to disconnect the said second source and to connect 'the first source.

24. In combination, a track section, a track circuit including a source of steady alternating current connected to the rails at one end of the section, a track relay having a winding connected in series with an impedance unit to the rails at the other end of the section,an armature for said track relay adapted to engage one or the other of a pair of contacts, means for at times to periodically vary the impedance of said unit to effect alternate engagement of said armature with said pair of contacts in step with said periodic variations of the impedance unit, a controlling relay, means to energize said controlling relay in response to the alternating engagement of said armature with said pair of contacts, and traffic governing means controlled by said controlling relay.

25. In combination, a signaling circuit for railways, a'sou'rce to supply'said circuit with alternating current,. a relay connected to the circuit at a point'remote from the source, an armaturev operated by said relay adapted to engage one orthe other of a pair of contacts, means located adjacent said relay to? at times periodically vary the value of the alternating current supplied by the circuit to the relay to effect alternate engagement of the armature with said pair of contacts, a controlling relay, means to retain said controlling relay energized in response to the alternating engagement of the armature with said pair of contacts, and traific governing means controlled by said controlling relay.

26. In combination, a track section, a first circuit to normally supply coded current to the trafiic rails at one end of the section, a track relay connected to the traflic rails at the opposite end of the section and responsive to such coded current in the rails, means responsive to a train entering the section at the end at which current is normally supplied to disconnect said first circuit and to connect a second circuit to supply non-coded current to the rails, means operated by the track relay when energized by non-coded current to open and close said second circuit to effect periodic energizing and deenergizing of the track relay, means controlled by the track relay when periodically energized and deenergized to restore the first circuit and to disconnect the second circuit.

27. In combination, a track section over which traffic may move in either direction, a first circuit to normally supply coded current to the rails at one end of the section, a track relay connected to the rails at the opposite end of the section and responsive to such coded current in the rails, a decoding relay, means to energize the decoding relay in response to the track relay periodically energized and deenergized and deenergize said decoding relay when the track relay is shunted, means responsive to a train entering the section at the end at which current is normally supplied to disconnect the first circuit and to connect a second circuit to supply the rails with non-coded current, means operated by the track relay when energized by said non-coded current to open and close said second circuit to effect a periodic energizing and deenergizing of the track relay to thereby reenergize the decoding relay, and means controlled by the decoding relay to restore the first circuit.

28. In combination, a track section over which traffic may move in either direction, a track transformer connected to the rails at one end of the section, a first circuit to normally supply the track transformer with alternating current periodically interrupted, a track relay connected to the rails at the opposite end of the section and responsive to such periodically interrupted alternating current, a decoding relay, means to energize the decoding relay when the track relay is periodically energized and deenergized and to deenergize said decoding relay when the track relay is shunted, means responsive to a train entering the section at the transformer end to disconnect the first circuit and to connect a second circuit to supply uninterrupted alternating current to the transformer, means operated by the track relay when energized by the uninterrupted alternating current to open and close said second circuit to effect a periodic energizing and deenergizing of said track relay to thereby reenergiz e said decoding relay, and

.means controlled by the decoding relay for restoring the first circuit.

29. In an absolute permissive block signaling system for railroads, the method of controlling detection code to a cab signal control code which control code comprises current periodically varied at a frequency selected in accordance with trafiic conditions in advance.

30. In combination, a section of railway track, a wayside signal associated with said section, means for normally supplying to the rails of said section a detection code for controlling said wayside signal, said code being supplied irrespective of traffic conditions in advance of the section and comprising rail current periodically varied at a given frequency, means governed by trafiic conditions in said section for transferring from said detection code to a cab signal control code comprising current periodically varied at a frequency selected in accordance with tramc conditions in advance of said section, and means governed by other traffic conditions in said section for restoring from said cab signal control code to said detection code.

31. In an absolute permissive block signaling system for railroads, the method of detecting the presence of a train in a track section and governing the train in accordance with traffic conditions in advance of the section, in which current periodically varied in accordance with a given detection code is supplied to the track rails of the section irrespective of traffic conditions in advance of the section for controlling wayside apparatus to provide said train detection, means being provided efiective upon the entry of a train into the section for transferring from said detection code to a selected one of a group of cab signal control codes employing periodically varied current, said selected code being determined in accordance with traffic conditions in advance of the section.

32. In combination, a section of railway track, two wayside signals for governing traffic in either direction through said section, a code following track relay connected with the rails at one end of said section for controlling said signals, means for supplying current to the rails at either end of the section, means for periodically varying the current supplied to the rails at the end of the section opposite said relay in accordance with a predetermined detection code for causing periodic operation of said relay to render effective the control of said wayside signals by the relay when said section is unoccupied, means effective when said section becomes occupied by a train entering from one or the other direction for periodically varying the current supplied to one or the other end of the section respectively in accordance with one of a group of cab signal control codes selected according to trafiic conditions in advance of the section, and means governed by the cab signal control code effective when the train vacates said section for restoring said detection code to the section.

selected in accordance with trafilc conditions in advance, and means for applying a selected code of said group to the rails of said section irrespective of trafiic conditions in advance of the section for train detection purposes when the section is unoccupied.

HOWARD A. THOMPSON. 

